Port Applications chooser from other plugs

[danirabbit]

The way this application chooser is done, it will be affected by the issue mentioned here: https://elementaryos.stackexchange.com/questions/14929/add-startup-app-menu-broken

We should make this chooser match the one from Applications and Security & Privacy

[peteruithoven]

It's actually not, since it's scrollbar has a better policy, it's actually what I used in the end to fix the AppChooser in the Applications and Security plugs. (See: https://github.com/elementary/switchboard-plug-applications/pull/15)

But it is quite a shame there we have similar code in 3 different plugs. Isn't there a way to share this code? I can imagine it would be a bit to specific to add to Granite for example?

One issue is that it looks different, for comparison:

[danirabbit]

I'm gonna close this since the approw has been abstracted here and the design matches other plugs